Particles of carboxylated polymer

ABSTRACT

Carboxyl group-containing polymer particles giving a neutralized viscous liquid being excellent in gel appearance and transparency. Carboxyl group-containing polymer particles comprising 55 to 94% by volume of water-swelled gel particles having a particle diameter of less than 50 μm when the carboxyl group-containing polymer particles are dispersed and swelled in water in a concentration of 0.5% by weight, and 6 to 45% by volume of water-swelled gel particles having a particle diameter of at least 50 μm when carboxyl group-containing polymer gel particles are dispersed and swelled in water in a concentration of 0.5% by weight.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP02/02745 which has an Internationalfiling date of Mar. 22, 2002, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to carboxyl group-containing polymerparticles. More specifically, the present invention relates to carboxylgroup-containing polymer particles which can be suitably used as athickener for cosmetics and the like, a suspension stabilizer foremulsions or suspensions, and the like; and a process for preparing thesame.

BACKGROUND ART

As a carboxyl group-containing polymer, there have been known acopolymer of an α,β-unsaturated carboxylic acid such as acrylic acid anda polyallyl ether (U.S. Pat. No. 2,923,692); a copolymer of anα,β-unsaturated carboxylic acid and hexaallyl trimethylene trisulfone(U.S. Pat. No. 2,958,679); a copolymer of an α,β-unsaturated carboxylicacid and triallyl phosphate (U.S. Pat. No. 3,426,004); a copolymer of anα,β-unsaturated carboxylic acid and glycidyl methacrylate (JapanesePatent Laid-Open No. Sho 58-84819); and the like. The particles of thesecarboxyl group-containing polymers have been used for uses such as athickener for cosmetics and a suspension stabilizer for emulsions orsuspensions, after the particles are dispersed and swelled in water, andneutralized with an alkali, to give a neutralized viscous liquid.

However, there are some defects in the neutralized viscous liquidsprepared by neutralizing the above-mentioned particles of the carboxylgroup-containing polymers with an alkali that gloss or the like isinsufficient because the gel appearance (surface smoothness) andtransparency of the liquids are insufficient. Therefore, if the gelappearance of a neutralized viscous liquid is excellent, there are somedefects that it takes a long period of time for agitation, and in somecases, at least 10 hours for mixing with agitation, which differsdepending upon the agitation apparatus or the agitation conditions usedfor the neutralization when the particles are neutralized with analkali, so that its productivity is not good.

DISCLOSURE OF INVENTION

The present invention has been accomplished in view of theabove-mentioned prior art. An object of the present invention is toprovide carboxyl group-containing polymer particles which give aneutralized viscous liquid being excellent in gel appearance andtransparency.

The present invention relates to:

-   (1) carboxyl group-containing polymer particles comprising 55 to 94%    by volume of water-swelled gel particles having a particle diameter    of less than 50 μm when the carboxyl group-containing polymer    particles are dispersed and swelled in water in a concentration of    0.5% by weight, and 6 to 45% by volume of water-swelled gel    particles having a particle diameter of at least 50 μm when the    carboxyl group-containing polymer particles are dispersed and    swelled in water in a concentration of 0.5% by weight; and-   (2) a process for preparing the carboxyl group-containing polymer    particles as defined in the above (1), comprising reacting 6 to 25    parts by volume of an α,β-unsaturated carboxylic acid based on 100    parts by volume of an inert solvent, with 0.15 to 2 parts by weight    of a compound having at least two ethylenic unsaturated groups based    on 100 parts by weight of the α,β-unsaturated carboxylic acid at 50°    to 90° C. in the inert solvent in the presence of 0.01 to 0.45 parts    by weight of a radical polymerization catalyst based on 100 parts by    weight of the α,β-unsaturated carboxylic acid.

BEST MODE FOR CARRYING OUT THE INVENTION

As described above, the carboxyl group-containing polymer particles ofthe present invention comprise 55 to 94% by volume of water-swelled gelparticles having a particle diameter of less than 50 μm when thecarboxyl group-containing polymer particles are dispersed and swelled inwater in a concentration of 0.5% by weight, and 6 to 45% by volume ofwater-swelled gel particles having a particle diameter of at least 50 μmwhen the carboxyl group-containing polymer particles are dispersed andswelled in water in a concentration of 0.5% by weight.

As described above, when the carboxyl group-containing polymer particlesof the present invention are dispersed in water in a given concentrationand swelled, the water-swelled gel particles of the carboxylgroup-containing polymer have a specified particle size distribution, sothat there are exhibited some excellent effects such that the gelappearance of the resulting neutralized viscous liquid becomesexcellent, and that there is obtained a neutralized viscous liquidhaving excellent transparency.

In the present invention, the reason why the carboxyl group-containingpolymer particles are dispersed in water so as to have a concentrationof 0.5% by weight and swelled is that the polymer particles aregenerally used in a concentration of at most 0.5% by weight in manycases and the gel appearance of a 0.5% by weight neutralized viscousliquid is remarked when used as cosmetics and the like.

In the present specification, the phrase “when the carboxylgroup-containing polymer particles are dispersed in water and swelled”means that the carboxyl group-containing polymer particles are dispersedin water and swelled, and the swelled particles are attained toequilibrated state. When the polymer particles are dispersed in waterand swelled, the temperature of the water is not limited to specifiedones. The temperature of the water is usually 20° to 30° C. or so.

The particle diameter of the water-swelled gel particles dispersed in aconcentration of 0.5% by weight is intended to mean a particle diameterdetermined by a laser diffraction type particle size distributionanalyzer (commercially available from Shimadzu Corporation under thetrade name of SALD-2000 J) after charging a 200-mL beaker with 149.25 gof ion-exchanged water at 25° C., gradually adding thereto 0.75 g ofcarboxyl group-containing polymer particles, while stirring with astirrer (length: 28 mm and thickness: 7 mm) at 600 rotations per minute,thereafter stirring the dispersion for 1.5 hours.

The content of the water-swelled gel particles having each particlediameter is obtained by determining the particle diameters and at thesame time, counting the number of gel particles having the particlediameter with the above-mentioned laser diffraction type particle sizedistribution analyzer, and multiplying the volume of one gel particle asregarded as spherical by the number of the particles.

The reason why the particle diameter of the water-swelled gel particlesis controlled to less than 50 μm, after the carboxyl group-containingpolymer particles are dispersed in a concentration of 0.5% by weight, isthat the gel appearance of the neutralized viscous liquid of thecarboxyl group-containing polymer particles is grainy if the particleshaving a particle diameter of at least 50 μm are contained in a largeamount. The particle diameter of the above-mentioned water-swelled gelparticles is preferably at least 0.1 μm and less than 50 μm from theviewpoint of improving the gel appearance of the neutralized viscousliquid of the carboxyl group-containing polymer particles.

The amount of the water-swelled gel particles having a particle diameterof less than 50 μm when the carboxyl group-containing polymer particlesare dispersed in water in a concentration of 0.5% by weight is at least55% by volume, preferably at least 58% by volume, more preferably atleast 60% by volume, from the viewpoint of improving the gel appearanceof the neutralized viscous liquid of the carboxyl group-containingpolymer particles. Also, the amount of the water-swelled gel particleshaving a particle diameter of less than 50 μm when the carboxylgroup-containing polymer particles are dispersed in water in aconcentration of 0.5% by weight is at most 94% by volume, preferably atmost 92% by volume, more preferably at most 90% by volume, from theviewpoint of increasing the transparency of the neutralized viscousliquid of the carboxyl group-containing polymer particles.

The reason why the particle diameter of the water-swelled gel particlesis controlled to at least 50 μm when the particles are dispersed inwater in a concentration of 0.5% by weight is that the transparency ofthe neutralized viscous liquid of the carboxyl group-containing polymerparticles is deteriorated if the particles having a particle diameter ofless than 50 μm are contained in a large amount. The particle diameterof the above-mentioned water-swelled gel particles is preferably atleast 50 μm and at most 300 μm from the viewpoint of increasing thetransparency of the neutralized viscous liquid of the carboxylgroup-containing polymer particles.

The amount of the water-swelled gel particles having a particle diameterof at least 50 μm, when the particles are dispersed in water in aconcentration of 0.5% by weight, is at most 45% by volume, preferably atmost 42% by volume, more preferably at most 40% by volume, from theviewpoint of improving the gel appearance of the neutralized viscousliquid of the carboxyl group-containing polymer particles. Also, theamount of the water-swelled gel particles having a particle diameter ofless than 50 μm is at least 6% by volume, preferably at least 8% byvolume, more preferably at least 10% by volume, from the viewpoint ofincreasing transparency of the neutralized viscous liquid of thecarboxyl group-containing polymer particles.

In consideration of the above viewpoints, when the carboxylgroup-containing polymer particles of the present invention aredispersed so as to have a concentration of 0.5% by weight, it is desiredthat the content of the water-swelled gel particles having a particlediameter of less than 50 μm, preferably at least 0.1 μm and less than 50μm is 55 to 94% by volume, preferably 58 to 92% by volume, morepreferably 60 to 90% by volume. Also, it is desired that the content ofthe water-swelled gel particles having a particle diameter of at least50 μm, preferably at least 50 μm and at most 300 μm is 6 to 45% byvolume, preferably 8 to 42% by volume, more preferably 10 to 40% byvolume.

The carboxyl group-containing polymer particles which give water-swelledgel particles having a specified particle size distribution mentionedabove when the polymer particles are dispersed in water in theabove-mentioned given concentration and swelled, can be obtained byreacting an α,β-unsaturated carboxylic acid in a specified amount with acompound having at least two ethylenic unsaturated groups in a specifiedamount at a specified temperature in the presence of a specified amountof a radical polymerization catalyst in an inert solvent.

The α,β-unsaturated carboxylic acid is not limited to specified ones,and includes, for instance, acrylic acid, methacrylic acid, crotonicacid, maleic acid, itaconic acid, fumaric acid, other olefinicunsaturated carboxylic acids, and the like. These carboxylic acids canbe used alone or in admixture of at least two kinds. Among them, acrylicacid is preferable because it is inexpensive and readily available andgives excellent transparency to the neutralized viscous liquid of thecarboxyl group-containing polymer particles.

The amount of the α,β-unsaturated carboxylic acid is 6 to 25 parts byvolume, preferably 8 to 22 parts by volume, more preferably 13 to 20parts by volume, based on 100 parts by volume of the inert solventdescribed below. When the amount of the α,β-unsaturated carboxylic acidis smaller than the above-mentioned lower limit, the transparency of theresulting neutralized viscous liquid of the carboxyl group-containingpolymer particles is lowered. Also, when the amount exceeds theabove-mentioned upper limit, the polymer particles are precipitated asthe reaction proceeds, thereby making it difficult to homogeneouslyagitate the mixture, so that the gel appearance of the resultingneutralized viscous liquid of the carboxyl group-containing polymerparticles is grainy.

The compound having at least two ethylenic unsaturated groups is notlimited to specified ones, and includes, for instance, acrylates ofpolyols having at least two substituted groups such as ethylene glycol,diethylene glycol, propylene glycol, polyoxyethylene glycol,polyoxypropylene glycol, glycerol, polyglycerol, trimethylolpropane,pentaerythritol, saccharose and sorbitol; methacrylates of polyolshaving at least two substituted groups; allyl ethers of polyols havingat least two substituted groups; diallyl phthalate, triallyl phosphate,allyl methacrylate, tetraallyloxyethane, triallyl cyanurate, divinyladipate, vinyl crotonate, 1,5-hexadiene, divinylbenzene, and the like.Among them, at least one member selected from the group consisting ofpentaerythritol tetraallyl ether, diethylene glycol diallyl ether andpolyallyl saccharose is preferable from the viewpoint of increasing thetransparency of the resulting neutralized viscous liquid of the carboxylgroup-containing polymer particles.

The amount of the compound having at least two ethylenic unsaturatedgroups is 0.15 to 2 parts by weight, preferably 0.3 to 1.5 parts byweight, based on 100 parts by weight of the α,β-unsaturated carboxylicacid. When the amount of the compound having at least two ethylenicunsaturated groups is smaller than the above-mentioned lower limit, theviscosity of the neutralized viscous liquid of the resulting carboxylgroup-containing polymer particles is lowered, and when the amountexceeds the above-mentioned upper limit, an insoluble gel is likely tobe produced in the resulting neutralized viscous liquid of the carboxylgroup-containing polymer particles .

The above-mentioned radical polymerization catalyst is not limited tospecified ones, and includes, for instance, azobisisobutyronitrile,2,2′-azobis-2,4-dimethylvaleronitrile, dimethyl-2,2′-azobisisobutyrate,benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tertiary butylhydroperoxide, and the like. Among them, azobisisobutyronitrile isfavorably used from the viewpoint of being easy to handle and excellentin stability.

The amount of the radical polymerization catalyst is 0.01 to 0.45 partsby weight, preferably 0.01 to 0.35 parts by weight, based on 100 partsby weight of the α,β-unsaturated carboxylic acid. When the amount of theradical polymerization catalyst is smaller than the above-mentionedlower limit, it is not economical because the reaction rate is lowered,and when the amount exceeds the above-mentioned upper limit, the gelappearance of the resulting neutralized viscous liquid of the carboxylgroup-containing polymer particles is grainy.

The inert solvent, as used herein, refers to a solvent which dissolvesthe α,β-unsaturated carboxylic acid and the compound having at least twoethylenic unsaturated groups but does not dissolve the carboxylgroup-containing polymer particles obtained.

The inert solvent includes, for instance, normal pentane, normal hexane,isohexane, normal heptane, normal octane, isooctane, cyclopentane,methylcyclopentane, cyclohexane, methylcyclohexane, benzene, toluene,xylene, chlorobenzene, ethylene dichloride, ethyl acetate, isopropylacetate, methyl ethyl ketone, methyl isobutyl ketone, and the like.These solvents can used alone or in admixture of at least two kinds.Among them, ethylene dichloride is preferable from the viewpoint ofbeing stable in quality and readily available.

It is preferable that the reaction of the α,β-unsaturated carboxylicacid with the compound having at least two ethylenic unsaturated groupsis carried out in the presence of an alkali metal carbonate togetherwith the radical polymerization catalyst. When the reaction is carriedout in the presence of the alkali metal carbonate together with theradical polymerization catalyst as mentioned above, the gel appearanceof the resulting neutralized viscous liquid of the carboxylgroup-containing polymer particles can be further improved.

The alkali metal carbonate includes sodium carbonate, potassiumcarbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, andthe like. Among them, sodium carbonate and potassium hydrogencarbonateare preferable because the lowering in the viscosity of the resultingneutralized viscous liquid of the carboxyl group-containing polymerparticles is small.

It is desired that the amount of the alkali metal carbonate is 0.01 to 5parts by weight, preferably 0.05 to 3 parts by weight, based on 100parts by weight of the α,β-unsaturated carboxylic acid from theviewpoint of improving the gel appearance of the neutralized viscousliquid.

The alkali metal carbonate can be added before the beginning of thereaction or during the course of the reaction. However, from theviewpoint of still more effectively improving the gel appearance of theneutralized viscous liquid of the carboxyl group-containing polymerparticles, it is preferable that the alkali metal carbonate is addedbefore the beginning of reaction.

It is preferable that the atmosphere where the α,β-unsaturatedcarboxylic acid is reacted with the compound having at least twoethylenic unsaturated groups is, for instance, an inert gas such asnitrogen gas or argon gas.

It is desired that the reaction temperature is 50° to 90° C., preferably55° to 75° C., from the viewpoint of lowering the viscosity of thereaction solution so that the solution can be agitated homogeneously,and from the viewpoint of improving the gel appearance of the resultingneutralized viscous liquid of the carboxyl group-containing polymerparticles.

The reaction time cannot be absolutely determined because the reactiontime differs depending upon the reaction temperature. The reaction timeis usually 2 to 10 hours.

After the termination of the reaction, white fine powder of carboxylgroup-containing polymer particles can be obtained by heating thereaction solution to 80° to 130° C. to remove the inert solvent byevaporation. In the case where the heating temperature exceeds 130° C.,there is a possibility that the gel appearance of the resultingneutralized viscous liquid of the carboxyl group-containing polymerparticles is grainy.

The carboxyl group-containing polymer particles of the present inventionare thus obtained. The powder of the carboxyl group-containing polymerparticles obtained is usually composed of secondary particles in whichprimary particles are aggregated.

When a neutralized viscous liquid is prepared using the carboxylgroup-containing polymer particles obtained, the polymer particles aredispersed in water so that the concentration of the carboxylgroup-containing polymer particles is usually 0.01 to 3% by weight, andthereafter the dispersion is neutralized with an alkali such as analkali metal hydroxide such as sodium hydroxide, or an amine such astriethanolamine or diisopropanolamine.

The neutralized viscous liquid obtained has excellent properties such asgel appearance and high transparency. The reason why this neutralizedviscous liquid has excellent properties as described above cannot beabsolutely determined. The reason will be presumably based on the factthat the secondary particles of the carboxyl group-containing polymerparticles are dispersed in water when the carboxyl group-containingpolymer particles are dispersed in water and swelled, and the carboxylgroup-containing polymer particles will exist in water as the primaryparticles of the water-swelled gel particles.

Next, the present invention will be explained more specifically on thebases of examples, without intending to limit the present invention onlyto those examples.

EXAMPLE 1

A 500 mL four-neck flask equipped with a stirrer, a thermometer, anitrogen gas inlet tube and a condenser was charged with 63 g (60 mL) ofacrylic acid, 0.44 g of pentaerythritol tetraallyl ether, 0.016 g ofazobisisobutyronitrile and 375 g (300 mL) of ethylene dichloride.Subsequently, the mixture was homogeneously mixed with stirring, andthereafter nitrogen gas was blown into the solution in order to removeoxygen existing in the upper space of the flask and the startingmaterials and the solvent. Next, the temperature of the mixture was keptat 70° to 75° C. under nitrogen atmosphere and reacted for 3 hours.

After the termination of the reaction, the resulting slurry was heatedto 110° C. to distill off ethylene dichloride. As a result, 63 g ofcarboxyl group-containing polymer particles were obtained.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined with a laser diffraction-type particle sizedistribution analyzer (manufactured by Shimadzu Corporation under theproduct number of SALD-2000J). As a result, the water-swelled gelparticles were composed of 0% by volume of particles having a particlediameter of less than 0.1 μm, 72% by volume of particles having aparticle diameter of at least 0.1 μm and less than 50 μm, 27.6% byvolume of particles having a particle diameter of at least 50 μm and atmost 300 μm, and 0.4% by volume of particles having a particle diameterexceeding 300 μm.

EXAMPLE 2

The same procedures as in Example 1 were carried out except that thecomponents charged to the four-neck flask were changed to 57.3 g (54.6mL) of acrylic acid, 0.66 g of pentaerythritol tetraallyl ether, 0.1 gof azobisisobutyronitrile and 525 g (420 mL) of ethylene dichloride, andthat the reaction temperature was changed to 55° to 60° C., to give 58 gof carboxyl group-containing polymer particles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 81% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 18.8% by volume of particles having a particle diameter of atleast 50 μm and at most 300 μm, and 0.2% by volume of particles having aparticle diameter exceeding 300 μm.

EXAMPLE 3

The same procedures as in Example 1 were carried out except that 0.75 gof diethylene glycol diallyl ether was used in place of 0.44 g ofpentaerythritol tetraallyl ether in Example 1, to give 63 g of carboxylgroup-containing polymer particles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 73% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 26.9% by volume of particles having a particle diameter of atleast 50 μm and at most 300 μm, and 0.1% by volume of particles having aparticle diameter of exceeding 300 μm.

EXAMPLE 4

The same procedures as in Example 1 were carried out except that 0.42 gof polyallyl saccharose was used in place of 0.44 g of pentaerythritoltetraallyl ether in Example 1, to give 63 g of carboxyl group-containingpolymer particles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 72% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 27.6% by volume of particles having a particle diameter of atleast 50 μm and at most 300 μm, and 0.4% by volume of particles having aparticle diameter exceeding 300 μm.

EXAMPLE 5

The same procedures as in Example 1 were carried out except that 0.5 gof sodium carbonate was charged together with the same components asused in Example 1, to give 64 g of carboxyl group-containing polymerparticles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 74% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 26% by volume of particles having a particle diameter at least 50μm and at most 300 μm, and 0% by volume of particles having a particlediameter exceeding 300 μm.

EXAMPLE 6

The same procedures as in Example 1 were carried out except that 0.9 gof sodium carbonate was charged together with the same components asused in Example 1, to give 65 g of carboxyl group-containing polymerparticles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 75% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 25% by volume of particles having a particle diameter of at least50 μm and at most 300 μm, and 0% by volume of particles having aparticle diameter exceeding 300 μm.

EXAMPLE 7

The same procedures as in Example 1 were carried out except that 1.8 gof sodium carbonate was charged together with the same components asused in Example 1, to give 64 g of carboxyl group-containing polymerparticles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 77% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 23% by volume of particles having a particle diameter of at least50 μm and at most 300 μm, and 0% by volume of particles having aparticle diameter exceeding 300 μm.

Comparative Example 1

The same procedures as in Example 1 were carried out except that thecomponents charged to the four-neck flask in Example 1 was changed to 30g (28.6 mL) of acrylic acid, 0.47 g of pentaerythritol tetraallyl ether,0.15 g of azobisisobutyronitrile and 411 g (328.8 mL) of ethylenedichloride, and that the reaction temperature was changed to 45° to 50°C., to give 30 g of carboxyl group-containing polymer particles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0.2% by volumeof particles having a particle diameter of less than 0.1 μm, 95% byvolume of particles having a particle diameter of at least 0.1 μm andless than 50 μm, 4.8% by volume of particles having a particle diameterof at least 50 μm and at most 300 μm, and 0% by volume of particleshaving a particle diameter exceeding 300 μm.

Comparative Example 2

The same procedures as in Example 1 were carried out except that thecomponents charged to the four-neck flask in Example 1 were changed to110.25 g (105 mL) of acrylic acid, 0.42 g of pentaerythritol tetraallylether, 0.007 g of azobisisobutyronitrile and 437.5 g (350 mL) ofethylene dichloride, to give 111 g of carboxyl group-containing polymerparticles.

An aqueous dispersion containing 0.5% by weight of the carboxylgroup-containing polymer particles was prepared, and the particle sizedistribution was determined in the same manner as in Example 1. As aresult, the water-swelled gel particles were composed of 0% by volume ofparticles having a particle diameter of less than 0.1 μm, 28% by volumeof particles having a particle diameter of at least 0.1 μm and less than50 μm, 69.2% by volume of particles having a particle diameter of atleast 50 μm and at most 300 μm, and 2.8% by volume of particles having aparticle diameter exceeding 300 μm.

[Evaluation of Physical Properties of Carboxyl Group-containing PolymerParticles]

Physical properties of the carboxyl group-containing polymer particlesobtained in Examples and Comparative Examples were evaluated on thebases of the following methods. The results are shown in Table 1.

(1) Gel Appearance

A 1-L beaker was charged with 483.3 g of ion-exchanged water, and 2.5 gof the carboxyl group-containing polymer particles were gradually addedthereto, while stirring with a stirrer (length: 5 cm and thickness: 1.5cm) at 600 rotations per minute. The mixture was stirred for additional1.5 hours, the stirrer was taken out from the flask, and 14.2 g of a 6%by weight aqueous sodium hydroxide was added thereto. The mixture wasstirred with an agitation blade as prescribed in CTFA (The CosmeticToiletry and Fragrance Association) for one hour, to give a neutralizedviscous liquid of carboxyl group-containing polymer particles.

The gel appearance of the neutralized viscous liquid of the carboxylgroup-containing polymer particles was visually evaluated. Theevaluation was made by a total of 10 male and female individuals asevaluation panelists, and the number of individuals of the panelists whohad an excellent feel for the evaluation on the gel appearance of theneutralized viscous liquid was totaled, and judged on the bases of thefollowing evaluation criteria. In the ordinary case, if the judgment isat least A in the following evaluation criteria, it can be evaluated tohave an excellent gel appearance.

[Evaluation Criteria] S: The number of individuals who had a feel thatthe gel appearance of the neutralized viscous liquid is excellent is 10;A: The number of individuals who had a feel that the gel appearance ofthe neutralized viscous liquid is excellent is 8 or 9; B: The number ofindividuals who had a feel that the gel appearance of the neutralizedviscous liquid is excellent is at most 7;(2) Transparency

A cell of 1 cm×1 cm was charged with the neutralized viscous liquid ofcarboxyl group-containing polymer particles obtained in theabove-mentioned (1), and transmittance was determined at a wavelength of425 nm. In the ordinary case, if the transmittance is at least 92%, itcan be evaluated to have excellent transparency.

(3) Viscosity

The viscosity of the neutralized viscous liquid of carboxylgroup-containing polymer particles obtained in the above-mentioned (1)was determined by a B-type rotary viscometer under the conditions ofRotor No. 7, 20 rotations per minute and a temperature of 25° C. In theordinary case, if the viscosity is 40000 mPa·s or more at 25° C., it canbe evaluated to have a high viscosity.

TABLE 1 Transparency Gel [Transmittance Viscosity Appearance (%)] (mPa ·s) Example No. 1 A 97 49000 2 S 96 49000 3 A 98 51000 4 A 98 45000 5 S97 46000 6 S 97 42000 7 S 97 40000 Comp. Ex. 1 S 80 42000 2 B 99 52000

It can be seen from the results shown in Table 1 that the neutralizedviscous liquids of the carboxyl group-containing polymer particlesobtained in Examples 1 to 7 are excellent in gel appearance andtransparency and have high viscosity, thereby making it useful as athickener.

INDUSTRIAL APPLICABILITY

The carboxyl group-containing polymer particles of the present inventionhave a specified particle size distribution when the carboxylgroup-containing polymer particles are dispersed in water to givewater-swelled gel particles. Therefore, the neutralized viscous liquidobtained is excellent in gel appearance and transparency. Also, sincethe neutralized viscous liquid has a high viscosity, the neutralizedviscous liquid is useful as a thickener for cosmetics and the like.

1. A process for preparing carboxyl group-containing polymer particles,comprising reacting 6 to 25 parts by volume of an α,β-unsaturatedcarboxylic acid based on 100 parts by volume of an inert solvent, with0.15 to 2 parts by weight of a compound having at least two ethylenicunsaturated groups based on 100 parts by weight of the α,β-unsaturatedcarboxylic acid at 50° to 90° C. in the inert solvent in the presence of0.01 to 0.45 parts by weight of a radical polymerization catalyst and0.01 to 5 parts by weight of an alkali metal carbonate based on 100parts by weight of the α,β-unsaturated carboxylic acid.
 2. The processfor preparing carboxyl group-containing polymer particles according toclaim 1, wherein the alkali metal carbonate is sodium carbonate orpotassium hydrogencarbonate.
 3. The process for preparing a carboxylgroup-containing polymer particle according to claim 1, wherein theα,β-unsaturated carboxylic acid is acrylic acid.
 4. The process forpreparing carboxyl group-containing polymer particles according to claim1, wherein the compound having at least two ethylenic unsaturated groupsis at least one member selected from the group consisting ofpentaerythritol tetraallyl ether, diethylene glycol diallyl ether andpolyallyl saccharose.
 5. The process for preparing carboxylgroup-containing polymer particles according to claim 1, wherein thecarboxyl group-containing polymer particles comprising 55 to 94% byvolume of water-swelled gel particles having a particle diameter of lessthan 50 μm when the carboxyl group-containing polymer particles aredispersed and swelled in water in a concentration of 0.5% by weight, and6 to 45% by volume of water-swelled gel particles having a particlediameter of at least 50 μm when the carboxyl group-containing polymerparticles are dispersed and swelled in water in a concentration of 0.5%by weight.